Nebulizer and a method of manufacturing a nebulizer

ABSTRACT

There is provided a nebulizer ( 2 ), comprising a first plate ( 20 ) configured to hold a transducer ( 14 ); a second plate ( 22 ) having an aperture therein, the first plate being positioned on a first side of the second plate such that the transducer is adjacent the aperture; and a third plate ( 24 ) configured to hold a mesh plate through which liquid can pass to form droplets, the third plate being positioned on a second side of the second plate opposite the first side such that the mesh plate ( 16 ) is adjacent the aperture, with the aperture, transducer and mesh plate forming a cavity for holding liquid to be nebulized. A method for manufacturing such a nebulizer is also provided.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C.§371 of International Application No. PCT/IB2013/053322, filed on Apr.26, 2013, which claims the benefit of U.S. Provisional PatentApplication No. 61/638,523, filed on Apr. 26, 2012. These applicationsare hereby incorporated by reference herein.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a nebulizer that nebulizes liquid held thereininto fine droplets, for example for inhalation by a user, and a methodof manufacturing thereof.

BACKGROUND TO THE INVENTION

Nebulizers, or atomizers as they are sometimes called, are devices thatgenerate a fine spray or aerosol from a liquid. A particularly usefulapplication for nebulizers is to provide a fine spray containing adissolved or a suspended particulate drug for administration to apatient by inhalation.

Since the patient has to administer a certain amount of medication, thetreatment time will be mainly determined by the mass flow rate of theaerosol generated by the nebulizer. Particularly for new medications,like biologics, the medication dose can be large, which means that thetreatment time can be up to several hours for nebulizers that arecurrently on the market.

However, so-called flat plate technology or piezo-cavity-mesh basednebulizers have the potential to offer much higher mass flow rates thanconventional nebulizers. In these types of nebulizers, a cavity for theliquid drug is created with an ultrasonic transducer forming one walland the other opposing wall of the cavity comprising an aperture or meshplate containing an array of nozzles or holes. When the transducer isactivated, ultrasonic pressure waves are created in the liquid in thecavity, causing liquid in the cavity to be pushed through the nozzles toform fine droplets.

One significant disadvantage with this type of nebulizer, however, isthat the mass flow rate achieved by the nebulizer is highly sensitive tothe distance between the transducer and the mesh plate. The mass flowrate for a particular flat plate technology nebulizer as a function ofthe distance between the transducer and mesh plate is shown in FIG. 1.Thus, it can be seen that the mass flow rate halves when the separation(referred to as the ‘height’ in FIG. 1) between the transducer and meshplate is 100 microns (0.1 mm) from the optimum separation (around 0.7mm).

The mass flow rate should be the same for each and every nebulizerproduced. Thus, a tolerance requirement is placed on nebulizers suchthat 90% of nebulizers built should have a mass flow rate within 25% ofthe target mass flow rate. This requirement can be fulfilled only whenthe tolerance of the separation distance is such that the standarddeviation of this distance is on the order of 10 microns (0.01 mm).

In addition, since the patient is administering medication to his or herlungs, care needs to be taken to keep the nebulizer clean. Residue fromthe liquids used in the nebulizer can lead to fouling and could become apotential health hazard. Moreover, this residue can subsequently clogthe nozzles in the mesh plate, decreasing the output performance of thenebulizer. For current nebulizers, it is recommended that the nebulizeris cleaned by rinsing with hot soapy water of 95° C. on a daily basis.This leads to a requirement for the nebulizer to be able to toleratearound 1800 of these cleaning cycles over its lifetime. Furthermore, theinterior of the nebulizer should be easily accessible while at the sametime any performance deterioration during the lifetime should beavoided. Therefore, a further desirable feature of the piezo-cavity-meshtype nebulizer is the ability to remove at least the mesh plate from thenebulizer for cleaning or replacement.

These requirements combined demand a nebulizer design that can bemanufactured with very small tolerances, high stability, and of course,low cost. These demands are hard to meet with conventional manufacturingtechnologies like injection-molding.

Therefore, there is a need for an alternative nebulizer and method ofmanufacturing thereof that meet these requirements.

SUMMARY OF THE INVENTION

Therefore, according to a first aspect of the invention, there isprovided a nebulizer, comprising a first plate configured to hold atransducer; a second plate having an aperture therein, the first platebeing positioned on a first side of the second plate such that thetransducer is adjacent the aperture; and a third plate configured tohold a mesh plate through which liquid can pass to form droplets, thethird plate being positioned on a second side of the second plateopposite the first side such that the mesh plate is adjacent theaperture, with the aperture, transducer and mesh plate forming a cavityfor holding liquid to be nebulized. By assembling the nebulizer from anumber of plates to form the cavity, the nebulizer can be manufacturedwith very small tolerances, high stability and low cost.

In some embodiments, the thickness of the second plate generally definesthe separation between the transducer and the mesh plate. Thus, bycontrolling the thickness of the second plate during manufacture, theseparation between the transducer and mesh plate can be set to thedesired amount to ensure efficient operation of the nebulizer.

In preferred embodiments, the nebulizer further comprises a foil layerdisposed between the first plate and the second plate to prevent contactbetween the transducer and liquid to be held in the cavity. Preferablythe foil layer is a metal foil since metallic foils absorb little of themechanical energy provided by the transducer.

In these embodiments, the combined thickness of the foil layer and thethickness of the second plate generally define the separation betweenthe transducer and the mesh plate. Thus, by controlling the thickness ofthe second plate and foil layer during manufacture, the separationbetween the transducer and mesh plate can be set to the desired amountto ensure efficient operation of the nebulizer.

Preferably, at least the second plate is metal. Metal is a preferredmaterial for the second plate as it is relatively easy to manufacturethe plates to the tolerances required in a nebulizer. Even morepreferably, at least the second plate is formed from rolled sheet metal.In preferred embodiments, at least the second plate is stainless steel,since this metal is cheap, thermally stable and won't be corroded orworn through contact with liquid in the cavity.

Preferably the third plate and mesh plate are removably attached to thesecond plate. This allows the third plate and mesh plate to be removedfor cleaning or replacement, and also allows access to the cavity forcleaning.

In some embodiments, the nebulizer further comprises a reservoir chamberfor holding further liquid to be nebulized, the reservoir chamber beinglinked to the cavity via a feed channel in the second plate that is influid communication with the first aperture in the second plate and ahole in the first plate.

Preferably at least a part of a lower edge of the hole in the firstplate has a jagged or saw-tooth profile, since this helps to encourageliquid to flow from the reservoir chamber through the hole and into thecavity.

In some embodiments, the second plate further comprises a ventingchannel for venting the cavity.

Preferably, the first plate and second plate are fixedly attachedtogether, for example using glue, adhesive or any other type of bondingmaterial or layer. In preferred embodiments, the first plate and secondplate are fixedly attached together using an adhesive or bonding layer,the adhesive or bonding layer comprising spacer particles therein forsetting the thickness of the adhesive or bonding layer to apredetermined amount. In these embodiments, the thickness of the secondplate and thickness of the adhesive or bonding layer (as determined bythe spacer particles) generally defines the separation between thetransducer and the mesh plate.

Where the nebulizer comprises a foil layer between the first plate andsecond plate, the foil layer can be attached to each of the first andsecond plates using a respective adhesive or bonding layer thatcomprises spacer particles. In these embodiments, the thickness of thesecond plate, foil layer and each of the adhesive or bonding layers (asdetermined by the spacer particles) generally defines the separationbetween the transducer and the mesh plate.

According to a second aspect of the invention, there is provided amethod of manufacturing a nebulizer, the method comprising obtaining asecond plate having an aperture therein; attaching a first plate that isconfigured to hold a transducer to a first side of the second plate suchthat the transducer is adjacent the aperture; and attaching a thirdplate that is configured to hold a mesh plate through which liquid canpass to form droplets to a second side of the second plate opposite thefirst side such that the mesh plate is adjacent the aperture, with theaperture, transducer and mesh plate forming a cavity for holding liquidto be nebulized.

In some embodiments, the step of obtaining a second plate comprisesobtaining a second plate having a predetermined thickness, with thethickness of the second plate generally defining the separation betweenthe transducer and the mesh plate. This enables the separation betweenthe transducer and mesh plate to be set to the desired amount to ensureefficient operation of the nebulizer.

In preferred embodiments, the step of attaching the first plate to afirst side of the second plate comprises disposing a foil layer betweenthe first plate and the second plate to prevent contact between thetransducer and liquid to be held in the cavity. Preferably the foillayer is a metal foil since metallic foils absorb little of themechanical energy provided by the transducer.

In these embodiments, the combined thickness of the foil layer and thethickness of the second plate generally define the separation betweenthe transducer and the mesh plate. This enables the separation betweenthe transducer and mesh plate to be set to the desired amount to ensureefficient operation of the nebulizer.

Preferably, at least the second plate is metal. Metal is a preferredmaterial for the second plate as it is relatively easy to manufacturethe plates to the tolerances required in a nebulizer. Even morepreferably, at least the second plate is formed from rolled sheet metal.In preferred embodiments, at least the second plate is stainless steel,since this metal is cheap, thermally stable and won't be corroded orworn through contact with liquid in the cavity.

Preferably the step of attaching the third plate to the second side ofthe second plate comprises removably attaching the third plate to thesecond plate. This allows the third plate and mesh plate to be removedfor cleaning or replacement, and also allows access to the cavity forcleaning.

In some embodiments, the method further comprises the steps of: forminga hole through the first plate, forming a feed channel in the secondplate, and attaching a reservoir chamber for holding further liquid tobe nebulized to the first plate, such that the reservoir chamber islinked to the cavity via the feed channel in the second plate and thehole in the first plate.

Preferably the step of forming a hole through the first plate comprisesforming a hole such that at least a part of a lower edge of the hole hasa jagged or saw-tooth profile, since this helps to encourage liquid toflow from the reservoir chamber through the hole and into the cavity.

In some embodiments, the method further comprises forming a ventingchannel for venting the cavity in the second plate.

Preferably, the step of attaching the first plate to the second platecomprises fixedly attaching the first and second plates together, forexample using glue, adhesive or any other type of bonding material orlayer. In preferred embodiments, the step of attaching the first plateand second plate comprises using an adhesive or bonding layer, with theadhesive or bonding layer comprising spacer particles therein forsetting the thickness of the adhesive or bonding layer to apredetermined amount. In these embodiments, the thickness of the secondplate and thickness of the adhesive or bonding layer (as determined bythe spacer particles) generally defines the separation between thetransducer and the mesh plate.

Where the step of attaching the first plate to the second platecomprises disposing a foil layer between the first plate and secondplate, the step of attaching can comprise using an adhesive or bondinglayer that comprises spacer particles to attach the foil layer to eachof the first and second plates. In these embodiments, the thickness ofthe second plate, foil layer and each of the adhesive or bonding layers(as determined by the spacer particles) generally defines the separationbetween the transducer and the mesh plate.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show more clearlyhow it may be carried into effect, reference will now be made, by way ofexample only, to the accompanying drawings, in which:

FIG. 1 is a graph illustrating the variation in mass flow rate of anebulizer with changes in the distance between the transducer and meshplate;

FIG. 2 is a block diagram of a piezo-cavity-mesh type nebulizeraccording to the invention;

FIG. 3 is an exploded view of a nebulizer according to an embodiment ofthe invention;

FIG. 4 shows two perspective views of a nebulizer according to anotherembodiment of the invention; and

FIG. 5 is a flow chart illustrating a method of manufacturing anebulizer according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 is a block diagram illustrating a general piezo-cavity-mesh typenebulizer 2 according to the invention. The nebulizer 2 comprises a body4 having an inlet 6 and an outlet 8 arranged so that when a user of thenebulizer 2 inhales through the outlet 8, air is drawn into and throughthe nebulizer 2 via the inlet 6 and outlet 8 and into the user's lungs.The outlet 8 is typically provided in the form of a mouthpiece or afacial or nasal mask or in a form that is suitable for connection to aseparate replaceable mouthpiece or facial or nasal mask.

The nebulizer 2 comprises a cavity 10 located adjacent to the conduitbetween the inlet 6 and outlet 8 for holding a liquid 12, for example amedication or drug, to be nebulized (i.e. to be turned into a fine mistor spray). The nebulizer 2 is configured such that fine droplets of thenebulized liquid 12 combine with the air drawn through the nebulizer 2when the user inhales to deliver a dose of the medication or drug to theuser.

One wall of the cavity 10 is formed by an actuator or transducer 14 andthe opposite wall of the cavity 10 facing the conduit between the inlet6 and outlet 8 is formed by a mesh plate 16. The mesh plate 16 isarranged so that liquid droplets passing therethrough enter the airdrawn in through the air inlet 6.

The transducer 14 is provided for agitating or vibrating the liquid 12held in the cavity 10. Preferably, the transducer 14 generatesultrasonic pressure waves in the liquid 12 held in the cavity 10. In theembodiments of the invention that are described further below, theactuator 14 is provided in the form of a piezoelectric element. However,those skilled in the art of nebulizers will appreciate that other formsof actuator 14 can be used in nebulizers according to the invention.

The mesh plate 16 is provided as a wall of the cavity 10 for nebulizingthe liquid 12 when the liquid 12 is vibrated by the transducer 14. Themesh plate 16 is typically in the form of a mesh or membrane having aplurality of small holes or nozzles through which small amounts of theliquid can pass. The size (diameter) of the nozzles in the mesh plate 16determines, among other things, the size of the droplets of liquidproduced when the nebulizer 2 is activated, and thus the mass flow rateof the nebulizer 2. The mesh plate 16 is removable from the nebulizer 2so that it can be cleaned or completely replaced, as required. The meshplate 16 is preferably formed from platinum, although those skilled inthe art will be aware of other suitable materials that can be used.Those skilled in the art will also appreciate that mesh plates 16 arealso known as aperture plates or nozzle plates.

In use, the liquid 12 fills the cavity 10 between the transducer 14 andmesh plate 16. It will be appreciated that the liquid 12 in the cavity10 will be depleted as the nebulizer 2 is operated, and more liquid 12must be added to the cavity 10 to maintain the liquid 12 at the requiredheight for the nebulizer 2 to continue operating. Therefore, thenebulizer 2 may comprise, or be coupled to, a reservoir chamber 18 thatstores liquid for replenishing the liquid 12 in the cavity 10. Theliquid from the reservoir chamber 18 may flow into the cavity 10 due tothe action of gravity and/or capillary filling.

The nebulizer 2 further comprises a control unit 19 that controls theoperation of the nebulizer 2, and in particular outputs signals to thetransducer 14 that cause the transducer 14 to vibrate at the requiredfrequency and nebulize the liquid 12.

FIG. 3 is an exploded view of a nebulizer 2 according to a preferredembodiment of the invention, showing the components required toconstruct a nebulizer 2 so that the required tolerance on transducer 14and mesh plate 16 separation is achieved.

As shown in FIG. 3, the nebulizer 2 comprises three plates 20, 22, 24that are to be assembled in a stack to form the main part of thenebulizer 2. The first plate, 20, referred to herein as the back plate20, has a hole 26 for receiving the transducer 14.

The second plate 22, referred to herein as the spacer plate 22,comprises an aperture 28 that forms the cavity 10 when the nebulizer 2is assembled. The aperture 28 is positioned in the spacer plate 22 sothat it is adjacent to the transducer 14 when the spacer plate 22, backplate 20 and third plate 24 are assembled to form a nebulizer 2.

The aperture 28 in the spacer plate 22 in the illustrated embodiment isgenerally circular as it is to approximately match the size of thetransducer 14 (which in this embodiment is also circular) so that thevolume of liquid in the cavity 10 exposed to the vibration of thetransducer 14 at any one time is maximized (thereby helping to increasethe mass flow rate provided by the nebulizer 2).

The third plate 24, referred to herein as the mesh plate holder 24,comprises the mesh plate 16. The mesh plate 16 is positioned in the meshplate holder 24 so that it is adjacent to the aperture 28 in the spacerplate 22 when the plates 20, 22, 24 are assembled into the nebulizer 2.

When the three plates are assembled, the mesh plate 16, mesh plateholder 24, aperture 28 and transducer 14 form the cavity 10 for holdingthe liquid 12 to be nebulized. The side of the transducer 14 facing thespacer plate 22 is typically aligned with the side of the back plate 20facing the spacer plate 22, and the side of the mesh plate 16 facing thespacer plate 22 is likewise aligned with the side of the mesh plateholder 24 facing the spacer plate 22. Thus, the thickness of the spacerplate 22 generally determines the separation between the transducer 14and mesh plate 16. In the example provided in FIG. 1, a spacer plate 22having a thickness of around 700 microns (0.7 mm) would be required inorder for the nebulizer 2 to achieve the maximum possible flow rate.

Preferably, at least the spacer plate 22 is formed from metal, since itis relatively easy to manufacture components from metal to thetolerances required in nebulizers 2 (e.g. a thickness to within 10microns) using known processes. Even more preferably, at least thespacer plate 22 is formed from rolled sheet metal. The aperture 28 andany other feature of the plate 22 can be formed using laser cuttingtechniques, although those skilled in the art will be aware of othertechniques that can be used. A suitable metal for use in forming atleast the spacer plate 22 according to the invention is stainless steelsince it is a relatively low-cost material, it is easy to work into aplate with the required thickness and cut-outs, it is wear resistant andshould maintain the required dimensions despite the nebulizer 2 beingfrequently dismantled for cleaning and then reassembled, and it is notlikely to be corroded or worn through contact with the liquids 12typically used in nebulizers 2. Stainless steel is also thermally stableso regularly heating the spacer plate 22 up to 95° C. during cleaningwill not alter the dimensions and performance of the nebulizer 2.Alternatively, at least the spacer plate 22 can be formed from titaniumor a titanium alloy (although these materials are not as low cost asstainless steel), or glass or a ceramic material (although these aremore fragile than metal).

The spacer plate 22 and back plate 20 are typically rigidly attached toeach other (for example using glue or another type of adhesive, bondingor fixing mechanism), so the spacer plate 22 and back plate 20 arepreferably formed from the same material, such as metal (e.g. stainlesssteel). Although the mesh plate 16 and mesh plate holder 24 are designedto be disposable items, and therefore it may be desirable to form themesh plate holder 24 from a cheaper material such as plastic, the meshplate holder 24 is preferably also formed from metal, such as stainlesssteel, in order to ensure that the required tolerances on transducer andmesh plate spacing are met.

Although not shown explicitly in FIG. 3, the mesh plate holder 24 isconfigured so that it can be detached and removed from the rest of thenebulizer 2 (i.e. spacer plate 22 and back plate 20) so that the meshplate 16 can be cleaned or the entire mesh plate holder 24 replaced. Tothis end, the spacer plate 22 or other component of the nebulizer 2 isprovided with a clamping or other attachment mechanism for holding themesh plate holder 24 in place adjacent to the spacer plate 22.

The back plate 20 can also include some clamping or other attachmentmechanism for retaining the transducer 14 in place in the nebulizer 2.Alternatively, the transducer 14 can be glued or otherwise rigidly fixedto the back plate 20 or spacer plate 22.

Where one of more of the components of the nebulizer 2 are adhered orbonded together (such as the back plate 20/transducer 14 to the spacerplate 22), the thickness of the bonding layer should be taken intoaccount when setting the distance between the transducer 14 and meshplate 16. That is, the distance between the transducer 14 and mesh plate16 will be equal to the thickness of the spacer plate 22 plus thethickness of any bonding layer(s), and the spacer plate 22 should bemanufactured accordingly. In preferred embodiments, the thickness of theadhesive or bonding layer is controlled by adding spacer particleshaving known (and highly precise) dimensions to the adhesive or bondingmaterial used to join the components together so that the spacerparticles define the spacing between the components.

Although in the illustrated embodiment the mesh plate 16 has a smallercross-sectional area than the aperture 28 and transducer 14, it will beappreciated that in other embodiments the cross-sectional area of themesh plate 16 can be generally the same as the aperture 28 andtransducer 14.

Furthermore, although FIG. 3 shows the mesh plate 16 as being separablefrom the mesh plate holder 24, it will be appreciated that the meshplate 16 is typically integrated into the mesh plate holder 24.

In the illustrated embodiment, a reservoir chamber 18 is attached to theback plate 20 (opposite the side of the back plate 20 that faces thespacer plate 22) to hold further liquid 12 that is to be nebulizedduring operation of the nebulizer 2. A second hole 30 is formed in theback plate 20 to allow liquid 12 to pass through the back plate 20 andinto the cavity 10.

Preferably, the second hole 30 does not have a fully rounded lower edge(since a fully rounded edge could form a barrier to liquid flow due tothe surface tension of the liquid 12), and therefore at least a part ofthe lower edge of the second hole 30 has a jagged or saw-tooth profilein order to ‘puncture’ the surface of the liquid 12 and improve the flowof liquid 12 through the second hole 30.

As shown, the aperture 28 in the spacer plate 22 that forms the cavity10 comprises a feed channel 32 to connect the cavity 10 between thetransducer 14 and mesh plate 16 to the reservoir chamber 18. It will beappreciated that although the feed channel 32 is shown in FIG. 3 ashaving been cut through the spacer plate 22, it is possible for the feedchannel 32 to be a groove or other indentation in the side of the spacerplate 22 facing the back plate 20.

It may be necessary to provide a vent through which air can escape whenthe cavity 10 is filled with liquid 12 from the reservoir chamber 18, sothe spacer plate 22 further comprises a relatively narrow ventingchannel 34 that extends from the aperture 28 to an edge (preferably atop edge) of the spacer plate 22. As with the feed channel 32, althoughthe venting channel 34 is shown in FIG. 3 as having been cut through thespacer plate 22, it is possible for the venting channel 34 to be agroove or other indentation in a side of the spacer plate 22.

To prevent any leakage of liquid 12 from the cavity 10 and feed channel32 when the nebulizer 2 is in use, a sealing component 36, such as arubber seal, can be provided between the spacer plate 22 and mesh plateholder 24. Preferably, to ensure that the sealing component 36 is heldin the correct position when the mesh plate holder 24 is assembled intothe nebulizer 2, a sealing component channel 38 is formed in the side ofthe mesh plate holder 24 that faces the spacer plate 22 that receivesthe sealing component 36.

Although not required in the embodiment shown in FIG. 3, in someembodiments a corresponding sealing component 36 can be provided betweenthe spacer plate 22 and the back plate 20. In this case, a correspondingsealing component channel 38 can be formed in the spacer plate 22 orback plate 20.

In some embodiments of the invention, the spacer plate 22 can beattached directly to the back plate 20, in which case the transducer 14can be covered with a metal, plastic or polymer protection layer toavoid direct contact between the transducer 14 and the liquid 12 in thecavity 10.

However, in preferred embodiments, a foil layer 40 is provided betweenthe spacer plate 22 and the back plate 20 that acts to separate thetransducer 14 from the liquid 12 in the cavity 10. In this preferredembodiment, the combined thickness of the foil layer 40 and spacer plate22 (and any adhesive layers, if present) determines the separationbetween the transducer 14 and the mesh plate 16. The foil layer 40 canhave similar dimensions (i.e. height and width) to the plates 20, 22, 24as shown in FIG. 3, but it will be appreciated that the foil layer 40 isconsiderably thinner than the plates 20, 22, 24.

The foil layer 40 is preferably a metal foil since metallic foils absorbvery little of the mechanical energy provided by the transducer 14compared to plastic or polymer-based layers. The metal foil could be anyhard biocompatible metal alloy, such as stainless steel. The foil layer40 can have a thickness of the range of 1-200 microns, for example 50microns. The foil layer 40 can be permanently attached to the back plate20 and/or spacer plate 22, for example using a glue, adhesive or otherbonding layer as described above (including spacer particles whereappropriate).

The thickness of the adhesive or bonding layer between the transducer 14and the foil layer 40 (or between the transducer 14 and the spacer plate22 in those embodiments where a foil layer 40 is not present) can bearound 50 micron. The thickness of the adhesive or bonding layer betweenthe foil layer 40 and the spacer plate 22 can be around 10 micron. Thethicker (or thick) layer of adhesive or bonding material between thetransducer 14 and the foil layer 40 (or spacer plate 22 in thoseembodiments where a foil layer 40 is not present) is desirable for anumber of reasons. Firstly, some transducers 14 comprise a disc ofsintered ceramics, and the surface roughness is on the order of 10s ofmicrons. Direct contact between the transducer 14 and metal (includingthe foil layer 40) should preferably be avoided, and therefore theadhesive or bonding layer can isolate the metal foil from the electriccharge on the electrode of the transducer 14. In addition, the adhesivelayer acts as a mechanical buffer, which is provided to absorb anystrain in the lateral direction due to the different expansioncoefficients of the transducer 14 and metal making up the foil layer 40(although in the described embodiments these coefficients are quitesimilar). By absorbing the strain, the peak stress is lowered such thatthe transducer 14 does not detach from the foil layer 40 under its ownaction (vibration) or during the high temperatures to which thenebulizer 2 is exposed during cleaning.

Where a reservoir chamber 18 is provided on the back plate 20, a hole 42is provided in the foil layer 40 that corresponds to the second hole 30in the back plate 20 to allow liquid 12 to flow from the reservoirchamber 18 into the cavity 10. Where the second hole 30 has a jagged orsaw-tooth lower edge, the hole 42 in the foil layer 40 will have acorresponding jagged or saw-tooth edge.

FIG. 4 shows two perspective views of a partially assembled nebulizer 2according to an alternative embodiment of the invention. In FIG. 4, theback plate 20, transducer 14, reservoir chamber 18, foil layer 40 andspacer plate 22 have been assembled into a unit, and this unit forms themain part of the nebulizer 2. The mesh plate 16 and mesh plate holder 24are detached from the main part of the nebulizer 2. The components inthe alternative embodiment of FIG. 4 generally correspond to theembodiment shown in FIG. 3, except that an alternative arrangement forsealing the mesh plate holder 24 to the spacer plate 22 is shown. Inthis arrangement, a sealing component 44 is provided that extends aroundthe periphery of the spacer plate 22.

An exemplary method of manufacturing part of a nebulizer 2 according tothe invention is shown in FIG. 5. In step 101, a spacer plate 22 isobtained (e.g. fabricated) from rolled sheet metal having a thicknessequal to the difference between the desired separation between atransducer 14 and a mesh plate 16 and the thickness of a foil layer 40to be used in the nebulizer 2 (if present), along with the thickness ofany adhesive or bonding layers used to assemble the components of thenebulizer 2 together. That is, the combined thickness of the spacerplate 22 and foil layer 40 (and adhesive layer(s)) is equal to thedesired separation between a transducer 14 and a mesh plate 16. Anaperture 28 is formed in the spacer plate 22 with dimensions that aresimilar to those of the transducer 14 to be used in the nebulizer 2. Theaperture 28 is to define a cavity 10 in the nebulizer 2 for holdingliquid 12 to be nebulized. The aperture 28 can be formed using lasercutting techniques.

In step 103, the metallic foil layer 40 is attached to one side of thespacer plate 22. The foil layer 40 can be attached to the spacer plate22 using glue or another type of adhesive, and can includehigh-precision spacer particles that act to define the thickness of theadhesive layer as described above.

In step 105, a back plate 20 and transducer 14 are attached to the foillayer 40 so that the transducer 14 is adjacent the aperture 28 in thespacer plate 22 and the foil layer 40 and transducer 14 form one wall ofthe cavity 10. Again, glue or another type of adhesive withhigh-precision spacer particles can be used to attach the back plate 20to the foil layer 40.

In step 107, which can occur during manufacture of the nebulizer 2and/or prior to use of the nebulizer 2 by a patient, a mesh plate 16 ina mesh plate holder 24 is attached to the opposite side of the spacerplate 22 to the foil layer 40 and back plate 20 so that the mesh plate16 forms the other wall of the cavity 10. As described above, the meshplate holder 24 is typically attached to the spacer plate 22 in such away as to allow removal and replacement of the mesh plate holder 24.Thus, the mesh plate holder 24 can be attached to the spacer plate 22using a clamping mechanism.

Although FIG. 5 illustrates some exemplary steps for manufacturing partof the nebulizer 2 according to the invention, those skilled in the artwill appreciate that a nebulizer 2 according to the invention can bemanufactured using different steps, or a different order or combinationof steps, to those illustrated. For example, step 103 could compriseattaching the foil layer 40 to the back plate 20 rather than to thespacer plate 22 with step 105 being adapted accordingly. Alternativelyor in addition, steps 103, 105 and 107 could be performed in a differentorder to that shown. Further steps in the method can comprise steps offabricating any one or more of the foil layer, back plate, mesh plate ormesh plate holder, including the fabrication of any channels or groovesin the plates for receiving a sealing component or for forming a ventingor feed channel.

Although the invention has been described in terms of a nebulizer thatis primarily for use in administering a medicament, it will beappreciated that the invention can be applied to any other type ofnebulizer or device in which a transducer is actuated in order tonebulize a liquid through a mesh plate, such as, for example an airhumidifier, an electric shaver, a steam iron or a perfume dispenser.

There is therefore provided a nebulizer that can be manufactured to therequired tolerances and is low cost.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments.

Variations to the disclosed embodiments can be understood and effectedby those skilled in the art in practicing the claimed invention, from astudy of the drawings, the disclosure and the appended claims. In theclaims, the word “comprising” does not exclude other elements or steps,and the indefinite article “a” or “an” does not exclude a plurality. Asingle processor or other unit may fulfill the functions of severalitems recited in the claims. The mere fact that certain measures arerecited in mutually different dependent claims does not indicate that acombination of these measures cannot be used to advantage. A computerprogram may be stored/distributed on a suitable medium, such as anoptical storage medium or a solid-state medium supplied together with oras part of other hardware, but may also be distributed in other forms,such as via the Internet or other wired or wireless telecommunicationsystems. Any reference signs in the claims should not be construed aslimiting the scope.

The invention claimed is:
 1. A nebulizer, comprising: a first plateconfigured to hold a transducer; a second plate having an aperturetherein, the first plate being positioned on a first side of the secondplate such that the transducer is adjacent the aperture; a third plateconfigured to hold a mesh plate through which liquid can pass to formdroplets, the third plate being positioned on a second side of thesecond plate opposite the first side such that the mesh plate isadjacent the aperture, with the aperture, transducer and mesh plateforming a cavity for holding liquid to be nebulized; and a reservoirchamber for holding further liquid to be nebulized, the reservoirchamber being linked to the cavity via a feed channel in the secondplate that is in fluid communication with the first aperture in thesecond plate and a hole in the first plate.
 2. A nebulizer as claimed inclaim 1, wherein at least a part of a lower edge of the hole in thefirst plate has a jagged or saw-tooth profile.
 3. A nebulizer as claimedin claim 1, the second plate further comprising a venting channel forventing the cavity.
 4. A nebulizer as claimed in claim 1, wherein thefirst plate and second plate are fixedly attached together.
 5. Anebulizer as claimed in claim 4, wherein the first plate and secondplate are fixedly attached together using at least one adhesive orbonding layer, the adhesive or bonding layer comprising spacer particlestherein for setting the thickness of the adhesive or bonding layer to apredetermined amount.
 6. A nebulizer as claimed in claim 1, wherein thethickness of the second plate generally defines the separation betweenthe transducer and the mesh plate.
 7. A nebulizer as claimed in claim 1,the nebulizer further comprising a foil layer disposed between the firstplate and the second plate to prevent contact between the transducer andliquid to be held in the cavity.
 8. A nebulizer as claimed in claim 7,wherein the foil layer is a metal foil.
 9. A nebulizer as claimed inclaim 7, wherein the thickness of the foil layer and the thickness ofthe second plate generally defines the separation between the transducerand the mesh plate.
 10. A nebulizer as claimed in claim 1, wherein atleast the second plate is metal.
 11. A nebulizer as claimed in claim 10,wherein at least the second plate is formed from rolled sheet metal. 12.A nebulizer as claimed in claim 10, wherein at least the second plate isrolled sheet stainless steel.
 13. A nebulizer as claimed in claim 1,wherein the third plate and mesh plate are removably attached to thesecond plate.
 14. A method of manufacturing a nebulizer, the methodcomprising: obtaining a second plate having an aperture therein;attaching a first plate that is configured to hold a transducer to afirst side of the second plate such that the transducer is adjacent theaperture; attaching a third plate that is configured to hold a meshplate through which liquid can pass to form droplets to a second side ofthe second plate opposite the first side such that the mesh plate isadjacent the aperture, with the aperture, transducer and mesh plateforming a cavity for holding liquid to be nebulized; and attaching areservoir chamber for holding further liquid to be nebulized, thereservoir chamber being linked to the cavity via a feed channel in thesecond plate that is in fluid communication with the first aperture inthe second plate and a hole in the first plate.